If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.

Serial Communication
Uses RS-232C standard with DB9 or DB25. Transmits data sequentially over a single conductor either synchronously or asynchronously. The Primary Synchronous Control Signals are:
Serial Data Out (TxD) - Used to Transmit Data.
Serial Data Receive (RxD) - Used to Receive Data.
Data Terminal Ready (DTR) - Used to tell receiver that data is ready to be sent. Connected to the DSR on the receiving hardware.
Data Set Ready (DSR) - Used on the Receiver to indicate it is ready.
System Ground - Ground Reference Voltage between two devices. Parallel Communication
Transmits data over eight conductors in parallel. Signals are either control signals or data signals. Control signals are used to synchronise the devices (Handshaking).

Primary Parallel Control Signals
Acknowledgement - Used to inform the transmitting device that data was received and the receiver is ready for more.
AutoFeed - Used to inform the printer to generate an auto line feed.
Busy - Used to inform sender that receiver is busy.
Error - Used by receiver to indicate an error.
Init - Used by sender to initialise the receiver.
Slct - Used by the receiver to ack a Slctln.
SlctIn - Used by the sender to select a device.
Strobe Asserted - Used by the receiver to inform that data is present on the lines.

Types of Connectors
Connectors are either Male (Pins) or Female (sockets).

IDE Devices
Integrated Drive Electronics are controllers for Hard Drives, CD-ROMS and any other compliant device. The Controller is on the device itself.
IDE < 528MB so EIDE (Enhanced) was developed.
Uses 40 Pin Cables.
Floppy uses 34 pin Cables.
CMOS has to be aware of the set-up of any E/IDE devices.
Normally two channels and only two devices can be on each channel.
Master/Slave
If more than one device is on a channel you have to set it to Master or Slave operation. This determines which controller takes precedent. This is set through jumpers.

SCSI Devices
Small Computer Systems Interface allows you to connect multiple devices to one cable. The Card is the controller so it removes overhead from the Drive itself and the CPU.

BIOS
Basic Input-Output System contains the system settings for the computer. These are stores on a memory chip located on the motherboard. The settings are removed from BIOS when you turn the computer off, but are restored from the CMOS at boot time. The CMOS is powered by the battery. (Complimentary Metal Oxide Semi-Conductor).
Flash BIOS means that the BIOS can be upgraded via a software Flash Program from the BIOS vendor.
Removable BIOS means that to Upgrade you have to physically remove and replace the BIOS chip.

System Optimization

Memory - Basically free up conventional memory between 0K and 640K. You can Load DOS into the high memory area by adding the following line to the CONFIG.SYS. DOS = HIGH. Another way to free up conventional memory is to load TSR’s into upper memory. To do this you must first load EMM386.EXE. You can then use DEVICEHIGH and LOADHIGH.
Hard Drives - Hard Drives become fragmented. De-Fragment them with the DOS command DEFRAG.
Cache Memory - To improve performance add more. Notes…
Never wear an electrostatic wrist strap when working near a monitor
Electricity comes into the house AC, Computers use DC
The DC current is fed to your computer in two forms +-5Vdc and +-12Vdc

Diagnosing and Troubleshooting
This section is concerned with the knowledge to diagnose and resolve various FRU faults.

POST Audible/Visible Error Codes
The Power On Self Test happens every time you boot the computer. It is used to diagnose system related problems that are found in hardware or BIOS. Anything other than a single beep indicates a fault.

Error RangeComponent

100-199
- System Board Problem

200-299
- Memory Error

300-399
- Keyboard Problem

400-499
- Video Problems, Monochrome

500-599
- Video problems, Colour

600-699
- Floppy Disk Errors

1700-1799
- Hard Disk Problems

Common Error CodesError CodeError MessageDescription

161
CMOS Battery Failure
CMOS Battery needs to be replaced

164
Memory Size Error
Occurs after a memory upgrade

201
Memory Test Failed
One or more of the RAM Chips failed

301
Keyboard Did Not Respond
Indication that the keyboard may need cleaning

303
Keyboard or System Unit Error
Indicates a bad keyboard that needs to be replaced

Cleaning
Liquid cleaning compounds such as isopopyl alcohol can be used to clean contacts and read/write heads via a cleaning diskette.
Rubber knifes can be used to remove hardened residue. Do not use metal knives.
Always vacuum out the case whenever you get the chance to reduce the build up of dust and also static electricity.

Power Issues
Brownouts – Momentary lapse in power.
Power Spike – Huge Increase in power for a split second.
Power Surge – Like a spike but lower power.

UPS
A UPS protects your PC from brownouts, spikes, surges and dirty current. This is accomplished by several components in the UPS such as suppressers, noise filters, and surge protectors.
Suppressers - Absorbs or blocks the spike and protects against surges.
Noise Filters - Noise caused by Electro-Magnetic Interference(EMI) is reduced.

CRT
Monitors are high voltage components. Never wear an ESD wrist strap when handling monitors.
To discharge a monitor, connect a wire around the screwdriver and ground the wire. Use the screwdriver to prise the anode lead from the back of the CRT.

Disposal Procedures:

* Batteries - Batteries should be disposed of in accordance with guidelines issued for your region. Never through them in the household waste.
* Toner Kits - Toner cartridges are recyclable. Normally the vendor will take these from you.
* Computers - Give away to charity or contact a specialist.
Material Safety Data Sheet(MSDS) - These are white pages that contain information on any substance that is deemed hazardous.

Electro-Static Discharge
This can cause catastrophic damage where the device is inoperable or it can cause degradation in a component which may still perform. Hidden ESD is a static discharge that you can not feel. You only feel ESD above 30,000 volts however components can still be damaged below 30,000 volts. To protect against ESD you can use ant-static mats, bags and an ESD wriststrap. You can ground the wrist strap to the earth pin on a wall socket. Also remove all metallic jewelery. Humidity below 50% leads to static.

Motherboard, Processors, Memory
This section is concerned with terminology and classifications of hardware.

CPU Chips:
8088 - Used an 8-bit bus and ran at 4.77MHz
386 - Could handle up to 16MB of memory. 386SX had a 16bit data bus and operated at 16, 20, 25, and 33 MHz. 386DX had a 32bit data bus and operated at 16, 20, 25, and 33 MHz.
486 - Four types the SX, DX, DX2 and DX4. The bus for all is 32bit. An 8bit on chip cache was introduced also a Maths Co-Processor was in-build but disables on the SX.
586(Pentium Class) - 64bit data bus, 16bit cache. Combines two 486DX chips into one using the Dual Independent Bus Architecture resulting in true parallel processing. Heat sinks were required due to the large amount of heat generated.
686(Pentium II Class) - Integrated MMX technology. Uses Slot 1 instead of a socket.

Random Access memory(RAM):

Static RAM(SRAM) - SRAM doesn’t have to be constantly refreshed. Uses a lot of power. Used in old IBM XT machines and was limited to 256K per chip.
Dynamic RAM(DRAM) - DRAM use capacitors instead of transistors and switches. Needs constant refresh.
Windows RAM(WRAM) - Specific to speed up graphical windows operations.
Extended Data Output RAM(EDO RAM) - Has a cache on the chip and is 10-15% faster than DRAM. Requires a special motherboard.
Memory comes in 30 or 72 pin SIMMs or 168 pin DIMMS

Bus Architectures:

Industry Standard Architecture(ISA) - This was introduced on AT computers. Allowed a 16-bit data bus. Used in 286 and 386SX PC’s.
Extended Industry Standard Architecture(EISA) - Introduced to compete against IBM’s MCA. Uses a 32-bit data bus. Used in 386DX and 486 PC’s.
Peripheral Component Interconnect(PCI) - Designed to use Pentium Processors. Uses a 64-bit data bus. Uses a bridge circuit to be processor independent.
Universal Serial Bus(USB) - A new technology for Plug and Play devices allowing up to 12Mbps.
VESA Local Bus(VL_Bus) - Used for Video cards on top of EISA.
Personal Computer Memory Card International Association(PCMCIA) - Now called PC Card. Used in Laptops. Currently only 16-bit data bus.
Complimentary Metal-Oxide Semiconductor(CMOS)
The BIOS can only hold setting when the machine is on. Once it loses power it loses the settings. Upon re-boot these are loaded from CMOS which is powered by a battery.

Basic CMOS Settings:

Printer Parallel Port
Unidirectional - Single direction communication.
Bi-directional – Two directional communication. Used by HP printers.
ECP(Extended Capability Port) – Same as Bi-directional but uses a DMA to bypass processor and speed up transfer.
EPP(Enhanced Parallel Port) – Same as bi-directional and offers an extended control code set.
COM/Serial Port
Memory Address – Each COM port requires a unique memory address.
IRQ - Every COM port requires a unique IRQ to talk to the CPU.
COM1 = IRQ4 and 03F8
COM2 = IRQ3 and 02F8
Hard Drives
Size – The Size is automatically detected by the computer.
Primary Master/Secondary Slave
Each hard drive has a controller built in the drive that controls the drive.
If two drives were on the same channel the adapter could get confused.
By setting one as a master it tells it which is in charge.
CDROMS
CDROMS on secondary channel alone are always set to slave.
Tracks – Each Ring.
Sector – Pie Slices.
Cylinder – Combination of identical tracks

Printers
This section explains the basic types of printers, concepts and how they work.

Types of Printers:
Daisy Wheel Printers
Uses impact method to imprint a character from a daisy wheel. Similar to a typewriter in operation. Excellent quality for text but no graphics. Uses a Ribbon

Dot Matrix Printers
Uses a matrix of pins to imprint an image. Uses a Ribbon. ROM programs the Fonts.

Bubble Jet Printers
Non Contact therefore quiet. Works by spraying ink onto the paper in a sequential fashion. Similar in operation to a dot matrix printer.

Laser Printers
Uses a Page Description Language (PDL) to print a page at a time. Main components are:
Cleaning Blade - This rubber blade removes excess toner off the drum after the print process has completed.
Photosensitive Drum - The core of the electrophotographic process. Involved in the six step EP process.
Primary Corona Wire - Highly negatively charged wire erases the charge on the Photosensitive drum to make it ready for another image.
Transfer Corona - A roller that contains a positively charged wire to pull the toner off the photosensitive drum and place it on the page.
Toner - Plastic Resin. Naturally Negatively charged
Fusing Rollers - Final stage of the EP process. Bonds the toner particles to prevent smearing. Uses heat to bond.

Electrophotographic Print Process(EP):
The process concerned with putting the image on the page. Follows Six processes.

Cleaning – The Drum is cleaned and electrically erased.
Charging – The Drum is negatively charged to –5000Vdc. Done by the Primary Corona.
Writing – The Laser sweeps the length of the drum applying the image. The Laser reduces the negative charge on the drum where the image is going to be.
Developing – The Toner is transferred to the area on the drum which has been swept by the laser.
Transferring - Once the image is on the drum the paper is fed through and the transfer corona wire attracts the image from the drum to the paper.
Fusing - The Fusing rollers heat up and pass the paper through bonding the toner to the paper. Uses a Non stick roller surface.

Troubleshooting:
Blank Pages - Can be caused by No Toner, Transfer Corona Failure or HVPS Failure.
Speckled Pages - Due to a failure in the cleaning step of the EP Process. Or a scratch on the EP drum.
Ghosted Images - Caused if the erasure lamp doesn’t erase all of the image from the EP drum before the next page is printed.
Smudged Images - The fusing process must have failed. The heating elements in the fusing rollers may be faulty.
Bubble Jet Printers - Never refill cartridges which are causing problems. The head is part of the cartridge so replace the entire cartridge.
Portable Systems
This section is concerned with the knowledge of Portable Computers and there hardware.

Lithium Ion (L-ION) – Good Power, Short Charge Time, Light, No Memory, Expensive.

Portable Displays
Older portables use CRT’s – Very Bulky, Heavy and poor quality. Nowadays Liquid Crystal Displays (LCD) are used. These are flat and lightweight. There are two major types of LCD screens:

Passive Matrix(Dual Scan) - Very Common, Low power but lower quality. Uses a grid of horizontal and vertical wires. These have problems with moving images and display ghosting.
Active Matrix(TFT) - Based on Thin Film Transistor (TFT) where a transistor is at every pixel. Allows a much quicker refresh but uses more power. Comparable in quality to a CRT.
LCD Displays are not serviceable but may be cleaned with specialist cleaning materials.

PCMCIA and PC Cards
PCMCIA or PC Card is a standard interface to add credit card sized peripherals to PC’s. Three versions are now available.

PCMCIA type I - Only used for memory cards. 68 Pin.
PCMCIA type II - Used for I/O devices such as Modems or Network Cards.
PCMCIA type III - Used for rotating mass storage such as hard drives.

A+ DOS/WINDOWS
DOS System Files:
DOS System files consist of:

AUTOEXEC.BAT - Located in the Root and automatically executed at start-up. Runs Programs (Prompt, WIN, CLS etc) and set commands (Path, Comspec etc..). Also calls other batch files. This is not required for OS Start-up.
CONFIG.SYS - Located in the Root and automatically loaded by MSDOS.SYS. This loads low level device drivers for hardware and memory drivers such as HIMEM.SYS and EMM386.EXE. This is not required for OS Start-up.
IO.SYS - Located in the Root and defines basic Input/Output routines for the processor. Is Hidden and Read Only. This IS required for OS start-up.
MSDOS.SYS - Located in the Root and defines system file locations. Is Hidden and Read Only. This IS required for OS start-up.
COMMAND.COM - This is the command specifier. It is responsible for the command prompt and contains all the internal commands such as DIR, COPY, and CLS. Located normally in the Root directory but can be located elsewhere and specified in the Autoexec.bat with a "SET COMSPEC=". This carries no attributes and is required for OS start-up.
HIMEM.SYS - Controls Extended Memory management in the extended memory area. Located in C:\DOS and is not required for OS start-up.
EMM386.EXE - Controls Expanded memory in the upper memory area. Located in C:\DOS and is not required for OS start-up.
ANSI.SYS - Located in C:\DOS and is used by CONFIG.SYS if required to load a character set. Not required for System Start-up.

WINDOWS 3.x
Windows 3.x System files consist of:

WIN.INI - Contains configuration information for Windows Applications. An ASCII text file located in the C:\WINDOWS directory. Looks after printing as well. Can cripple the system.
SYSTEM.INI - Contains specific system and hardware settings for windows. An ASCII text file located in the C:\WINDOWS directory. Errors can cripple or make Windows inoperable.
Three files make up the Windows core components: Kernel, User, and GDI. The kernel files (KRNL286.EXE or KRNL386.EXE) control and allocate all the computer resources to manage memory, load applications, and schedule program execution and other tasks.

USER.EXE - creates and maintains windows on the screen, carrying out all requests to create, move, size, or remove a window. USER.EXE also handles requests regarding the icons and other components of the user interface. USER.EXE directs input to the appropriate application from the keyboard, mouse, and other input sources.
GDI.EXE - controls the Graphics Device Interface, which executes graphics operations that create images on the system display and other devices.
WIN.COM - This is the actual file that runs Windows 3.x. It is made during install and cannot be found on any installation disk.
WIN.COM performs three functions.
Find out what processor is in the computer.
Switch to the appropriate graphics mode and display the *.LGO file.
Load the Windows Graphics Advert. This is an .RLE file.

WINDOWS 95:
Windows 95 System files consist of:

IO.SYS - Same as for DOS. This is because WINDOWS 95 is bootable.
MSDOS.SYS - Same as for DOS but doesn’t contain system code.
COMMAND.COM - Same as for DOS.
WIN.INI - For 16-bit compatibility.
SYSTEM.INI - For 16-bit compatibility.
SYSTEM.DAT - Hardware related Registry.
USER.DAT - User related Registry.

OS Start-up EnvironmentsWindows 3.x:

DOS loads first.
User enters WIN.COM
WIN.COM checks Processor, Graphics Mode , Loads Banner then passes to WIN386.EXE
WIN386.EXE switches CPU to Protected Mode.
The Kernel is Loaded.
Reads SYSTEM.INI
Loads Drivers.
Graphics Subsystem is loaded (GDI.EXE and USER.EXE)
Desktop Manager is started (PROGMAN.EXE).
WIN.INI is read and PROGMAN.INI
Windows 95 runs in a very similar way but WIN95 only supports protected mode and no switch exists for real mode.
Also there is a reliance on the registry.

Memory Management

First 640k is Conventional Memory
640k to 1024k is Upper Memory
Above 1024k is Extended Memory
HIMEM.SYS is loaded in CONFIG.SYS as the first driver to manage the Extended Memory are and to convert this to XMS (Extended Memory Specification). The first 64k of extended memory has been labelled High Memory (HMA). DOS can be put here by putting DOS=HIGH in CONFIG.SYS.
EMM386.EXE is loaded in CONFIG.SYS after HIMEM.SYS has been successfully loaded. This is used in the hardware reserved 384k of space in upper memory (640k-1024k) and creates EMS(Extended Memory Specification).
Virtual Memory relies upon EMS (therefore EMM386.EXE) and uses hard disk space as memory.

know how to sell your wares. intrinsic quality isnt enough. not everyone bites at substance or looks for inner value. people like to follow the crowd;they go someplace because they see other people do so. uniqueness appeals both to the taste and to the intellect.

It's a long post but I thought it would come in handy. I'm werking on my A+ and CCNA certs and thought this would be a good place to start. I need to fix the underline tags. I had to edit this post 6 times last night cause I didn't close all the bold tags and the italics. Any who, hope this helps.

For those who are taking the A+ test, the test has changed quite a bit.
The test no longer consists of 60-80 questions on each of the 2 tests. They're 30 questions and each questions weigthed on the level of difficulty of the question, and since it's 30, there's a greater chance of failure. Also, a policy has changes, once you take the first part, there is no alloted time for you to take the 2nd part. You can now take the 2nd part whenever you feel the need.

Originally posted here by sargx out of curiosity, is there still a growing demand for people with A+ certifications? I was tempted to get one, but I figured a BS in CS would kind of negate it's usefulness.

Might sound old fashioned, but if you apply for a job with a BS in CS and somebody else does and has the same education as you do but also an A+ certification, chances are they will hire your opponent.

heh, i got so bored of my A+ class. they didnt do jack on the networking patr of the exam and the rest of my classmates couldnt pass it cause of the damn teacher. i never tried to take the test, never got the time really, and besides, who cares for a civilian certification when i am certified to manage tactical LANs for the army?